Powertrain pressure and flow control system for dog clutches

ABSTRACT

A pressure and flow control system for a dog clutch includes a pilot valve, a regulating valve, and a selector. The pilot valve is configured to produce a pilot signal and includes a first valve, which is a MEMS microvalve. The regulating valve is in fluid communication with the pilot valve, and is configured to receive the pilot signal. The regulating valve is further configured to output a control signal. The selector is configured to engage and disengage the dog clutch in response to the control signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/393,393, filed on Oct. 15, 2010, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to hydraulic control of powertrains,transmissions, and the hydraulically-controlled components thereof.

BACKGROUND

Vehicle powertrains may include transmissions to transfer power andtorque from an engine to the vehicle output (axles or wheels). Hybridpowertrains may include multiple primary movers, including internalcombustion engines or alternative power sources, such as one or moreelectric machines coupled with an energy storage device. When thepowertrain is equipped with an additional primary mover, such as anelectric machine, the transmission may also transfer torque and powerfrom the electric machine to provide traction for the vehicle. Fixedgears or speed ratios of the transmission allow the engine to operatewithin a narrow range of speeds while providing a wide range of outputspeeds to the powertrain.

Different gears or operating modes of the transmission providedifferent, selectable speed ratios or gear ratios, and also differentlevels of torque multiplication. Changing the speed ratio of thetransmission generally changes the ratio of input speed to the outputspeed and changes the torque multiplication between the input and theoutput. Selection of speed ratios may occur through actuation ofhydraulic components controlled by one or more hydraulic valves. Thehydraulic pressure and flow regulated or provided by these valvesselects the requested speed ratio.

SUMMARY

A pressure and flow control system for a dog clutch is provided. Thepressure and flow control system includes a pilot valve, a regulatingvalve, and a selector. The pilot valve includes a first valve, and isconfigured to produce a pilot signal. The first valve is a Micro ElectroMechanical Systems (MEMS) microvalve. The regulating valve is in fluidcommunication with the pilot valve. The regulating valve is configuredto receive the pilot signal from the pilot valve and is configured tooutput a control signal, which controls the selector.

The regulating valve may be a MEMS-based spool valve or may be a smallmechanical spool valve. The pilot valve may further include a secondvalve, and the regulating valve may be a conventional mechanicalregulating valve. The second valve may be a MEMS-based spool valve ormay be a small mechanical spool valve.

The selector may be configured to engage and disengage the dog clutch inresponse to an on/off signal. The control signal from the regulatingvalve may be configured as the on/off signal. Furthermore, an on/offvalve may be disposed between the regulating valve and the selector, andthe on/off valve may be configured to convert the control signal to theon/off signal.

The above features and advantages, and other features and advantages, ofthe present invention are readily apparent from the following detaileddescription of some of the best modes and other embodiments for carryingout the invention, as defined in the appended claims, when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a Micro Electro MechanicalSystems (MEMS) microvalve actuator;

FIG. 2 is a schematic cross-sectional view of a MEMS spool valve whichmay be used alone or in conjunction with the MEMS microvalve actuatorshown in FIG. 1;

FIG. 3A is a schematic diagram of a powertrain having a transmissionwith at least one synchronized dog clutch, into which one or morepressure/flow control systems may be incorporated;

FIG. 3B shows a schematic isometric view of a synchronized dog clutchcontrolled by a selector fork, which may be incorporated into thetransmission 300 shown in FIG. 3A;

FIG. 3C shows a schematic partial-cutaway, exploded isometric view of asynchronized dog clutch controlled by an axial piston, which may beincorporated into the transmission 300 shown in FIG. 3A;

FIG. 4 is a schematic box diagram of a first option for a pressure/flowcontrol system for a hydraulically-controlled component within thepowertrain;

FIG. 5 is a schematic box diagram of a second option for a pressure/flowcontrol system for the hydraulically-controlled component within thepowertrain;

FIG. 6 is a schematic box diagram of a third option for a pressure/flowcontrol system for the hydraulically-controlled component within thepowertrain; and

FIG. 7 is a schematic box diagram of a fourth option for a pressure/flowcontrol system for the hydraulically-controlled component within thepowertrain.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numbers correspond tolike or similar components throughout the several figures, there isshown in FIG. 1 schematic cross-sectional view of a Micro ElectroMechanical Systems (MEMS) microvalve actuator 100. As discussed herein,the MEMS microvalve 100 may be used to effect hydraulic control—bycontrolling pressure or flow of a fluid—over one or more hydrauliccomponents, such as those within a transmission. The MEMS microvalve 100shown is only one type of MEMS device that may be used as a controlvalve or control actuator for the hydraulic components, and others,discussed herein. The MEMS microvalve 100 may also be referred to as apressure differential actuator or a pilot direct actuating valve (PDA).

While the present invention may be described in detail with respect toautomotive applications, those skilled in the art will recognize thebroader applicability of the invention. Those having ordinary skill inthe art will recognize that terms such as “above,” “below,” “upward,”“downward,” et cetera, are used descriptively of the figures, and do notrepresent limitations on the scope of the invention, as defined by theappended claims.

Generally, MEMS may be considered a class of systems that are physicallysmall, having features with sizes in the micrometer range. MEMS systemsmay have both electrical and mechanical components. MEMS devices areproduced through micromachining processes. The term “micromachining”generally refers to the production of three-dimensional structures andmoving parts through processes including modified integrated circuit(computer chip) fabrication techniques (such as chemical etching) andmaterials (such as silicon semiconductor material). The term“microvalve” as used herein generally refers to a valve having featureswith sizes in the micrometer range, and thus by definition is at leastpartially formed by micromachining The term “microvalve device” as usedin this application means a device that includes a microvalve, and thatmay include other components. MEMS devices may be operating inconjunction with other MEMS (micromachined) devices or components or maybe used with standard sized (larger) components, such as those producedby mechanical machining processes.

Referring to FIG. 1, the MEMS microvalve 100 includes a housing or body110. The MEMS microvalve 100 may be formed from several layers ofmaterial, such as semi-conductor wafers. The body 110 may also be formedfrom multiple layers. For example, and without limitation, thecross-sectioned portions shown may be taken through a middle layer ofthe MEMS microvalve 100, with two other layers existing behind and infront of (relative to the view in FIG. 1) the middle layer. The otherlayers of the body 110 may include solid covers, port plates, orelectrical control plates. However, each of the layers is generallyconsidered part of the body 110, except where separately identified.

The MEMS microvalve 100 includes a beam 112 actuated by a valve actuator114. Selective control of the actuator 114 causes the beam 112 to alterthe flow of fluid between an inlet port 116 and an outlet port 118. Byvarying the fluid flow between the inlet port 116 and the outlet port118, the MEMS microvalve 100 varies the pressure in a pilot port 120. Asdescribed herein, the pilot port 120 may be connected to additionalvalves or devices in order to effect hydraulic control thereof through apilot signal, which varies based upon the pressure and flow communicatedthrough the pilot port 120.

The inlet port 116 is connected to a source of high-pressure fluid suchas a pump (not shown). The outlet port 118 is connected to alow-pressure reservoir, sump, or fluid return (not shown). For purposesof the description herein, the outlet port 118 may be considered to beat ambient pressure, and acts as a ground or zero state in the MEMSmicrovalve 100.

The beam 112 moves in a continuously variable manner between a firstposition, illustrated in FIG. 1, a second position (not shown), andmyriad intermediate positions. In the first position, the beam 112 doesnot completely block the inlet port 116. However, in the secondposition, the beam 112 blocks the inlet port 116 to preventsubstantially all flow from the high-pressure fluid source.

A first chamber 122 is in fluid communication with both the inlet port116 and the outlet port 118. However, communication between the outletport 118 and the first chamber 122 (and also the inlet port 116) isrestricted by an outlet orifice 124. High pressure or fast fluid flowthrough the outlet orifice 124 causes a pressure differential to buildbetween the first chamber 122 and the outlet port 118.

The beam 112 is pivotally mounted to a fixed portion of the body 110 bya flexure pivot 126. The opposite portion of the beam 112 from theflexure pivot 126 is a movable end 128, which moves up and down (asviewed in FIG. 1) to selectively and variably cover and uncover theinlet port 116.

When the beam 112 is in the second position, it allows little or no flowfrom the inlet port 116 to the first chamber 122. Any pressurized fluidin the first chamber 122 bleeds off through the outlet orifice 124 tothe outlet port 118. As the beam 112 of the MEMS microvalve 100 is movedtoward the first (open) position, the inlet port 116 is progressivelyuncovered, allowing faster flows of fluid from the inlet port 116 intothe first chamber 122. The fast-flowing fluid cannot all be drainedthrough the outlet orifice 124 and causes a pressure differential toform as the fluid flows through the outlet orifice 124, raising pressurein the first chamber 122.

As the inlet port 116 is further opened to the first position (as shownin FIG. 1), fluid gradually flows faster through the outlet orifice 124,causing a larger pressure differential and further raising the pressurein the first chamber 122. When the beam 112 is in the first position, itallows high flow from the inlet port 116 to the first chamber 122.Therefore, the pressure in the first chamber 122 can be controlled bycontrolling the rate of flow from the inlet port 116 through the firstchamber 122 and the outlet orifice 124 to the outlet port 118. Theposition of the beam 112 controls the rate of flow of the fluid from theinlet port 116, and thus the pressure in the first chamber 122.

The valve actuator 114 selectively positions the beam 112. The actuator114 includes an elongated spine 130 attached to the beam 112. Theactuator 114 further includes a plurality of first ribs 132 and aplurality of second ribs 134, which are generally located on opposingsides of the elongated spine 130. Each of the first ribs 134 has a firstend attached to a first side of the elongated spine 130 and a second endattached to the body 110. Similar to the first ribs 132, each of thesecond ribs 134 has a first end attached to the elongated spine 130 anda second end attached to the fixed portion of the body 110.

The elongated spine 130, the first ribs 132, and the second ribs 134 areformed from the same material and are connected to the body 110 at somepoint, but are configured to allow relative movement of the elongatedspine 130. The connection may be below the cross-sectioned plane shownin FIG. 1. Generally, the elongated spine 130, the first ribs 132, andthe second ribs 134 may be considered the moving portions of theactuator 114.

The first ribs 132 and the second ribs 134 are configured to thermallyexpand (elongate) and contract (shrink) in response to temperaturechanges within the first ribs 132 and the second ribs 134. Electricalcontacts (not shown) are adapted for connection to a source ofelectrical power to supply electrical current flowing through the firstribs 132 and the second ribs 134 to thermally expand the first ribs 132and the second ribs 134.

The actuator 114 is adapted to be controlled by an electronic controlunit (ECU) or other programmable device (not shown in FIG. 1) whichsupplies variable current to the first ribs 132 and the second ribs 134.As the first ribs 132 and the second ribs 134 expand due to sufficientcurrent flow, the elongated spine 130 moves, slides, or stretchesdownward (as viewed in FIG. 1), causing the beam 112 to rotate in thegenerally counter-clockwise direction. The resulting movement of thebeam 112 causes the moveable end 128 to move upward (as viewed inFIG. 1) and progressively block more of the inlet port 116.

Closing the inlet port 116 allows less (and eventually no) fluid to flowinto the first chamber 122, decreasing the pressure therein as the fluiddrains to the outlet port 118. Once the inlet port 116 is closed, theMEMS microvalve 100 is in the second position (not shown), and no pilotsignal is being communicated through the pilot port 120.

As the flow of current drops, the first ribs 132 and the second ribs 134contract and the elongated spine 130 moves upward (as viewed in FIG. 1),causing the beam 112 to rotate in the generally clockwise direction. Theresulting movement of the beam 112 causes the moveable end 128 to movedownward (as viewed in FIG. 1) and progressively open more of the inletport 116.

Opening the inlet port 116 allows more fluid to flow into the firstchamber 122, increasing the pressure therein as the fluid flow overcomesthe ability of the outlet port 118 to drain fluid from the first chamber122. Once the inlet port 116 is substantially open, the MEMS microvalve100 is in the first position (shown in FIG. 1), and a relatively strongpilot signal is being communicated through the pilot port 120.

In addition to the heat-actuated MEMS device shown in FIG. 1, othertypes of MEMS or MEMS-based actuators may be used in place of the MEMSmicrovalve 100 or in place of the actuator 114. In general, themicro-electrical-mechanical system (MEMS) based device may include anydevice that has one or more electronic elements fabricated through anintegrated circuit technique (e.g., etching on a silicon wafer) and oneor more mechanical elements fabricated through a micromachining process(e.g., forming structures and moving parts with dimensions in themicrometer range). The electronic and mechanical elements may also beformed by other processes. In alternative or additional approaches,configurations, or embodiments, the MEMS-based device may include otherelements with dimensions in the micrometer range, such as anelectromagnetic field actuator, a piezoelectric amplifier, a thermalactuator, a pressure sensor, a gyroscope, an optical switch, otherMEMS-based devices, or any combination thereof.

Referring now to FIG. 2, and with continued reference to FIG. 1, thereis shown a schematic cross-sectional view of a MEMS-based spool valve200. The MEMS-based spool valve 200 includes a housing or body 210. TheMEMS-based spool valve 200 may be formed from several layers ofmaterial, such as semi-conductor wafers. The body 210 may also be formedfrom multiple layers. For example, and without limitation, thecross-sectioned portions shown may be taken through a middle layer ofthe MEMS-based spool valve 200, with two other layers existing behindand in front of (relative to the view in FIG. 2) the middle layer.

The MEMS-based spool valve 200 includes a slider 212 configured to bemovable to the left and to the right (as viewed in FIG. 2) within acavity 214 defined by the body 210. The slider 212 is actuated by fluidpressure on a piloted surface 216, which is in fluid communication witha piloted chamber 220 of the cavity 214. Selective variation of pressurewithin the piloted chamber 220 alters the force applied to the pilotedsurface 216. The piloted chamber 220 may be in fluid communication witha pilot signal, such as the pilot signal produced by the pilot port 120of the MEMS microvalve 100 shown in FIG. 1.

The slider 212 is formed with an elongated plate having a pair ofoppositely disposed arms extending perpendicularly at a first end of thebody so that the slider 212 is generally a T-shape, having the pilotedsurface 216 at a wider longitudinal end of the slider 212, and a countersurface 222 at a relatively-narrower opposing longitudinal end of theslider 212. The cavity 214 is also generally a T-shape.

The body 210 defines a number of ports connecting with the cavity 214,some of which may be formed in the cross-sectioned layer and some ofwhich may be formed in other layers. The ports include a supply port224, which is adapted to be connected to a source of high pressurefluid, such as a transmission pump (not shown). The supply port 224 maybe connected to the same source of high-pressure fluid as the inlet port116 of the MEMS microvalve 100 shown in FIG. 1. The body 210 alsodefines a tank port 226, which is connected to a low-pressure reservoiror fluid return (not shown). The tank port 226 may be connected to thesame source of low-pressure fluid as the outlet port 118 of the MEMSmicrovalve 100 shown in FIG. 1.

A first load port 228 and a second load port 230 are formed in the bodyand communicate with the cavity 214. The first load port 228 and thesecond load port 230 are disposed on opposite sides of the supply port224. The first load port 228 and the second load port 230 are adapted tobe connected together to supply pressurized fluid to ahydraulically-operated component of the transmission or powertrain, asdescribed herein. Additional ports, channels, or troughs (not viewablein FIG. 2) may be formed on the upper surface of the cavity 214 oppositethe first load port 228 and the tank port 226. The additional troughshelp balance flow forces acting on the slider 212.

The slider 212 shown includes three openings therethrough. A firstopening 232, close to the piloted surface 216, is defined through theslider 212 to permit the fluid volume to equalize through the troughabove the tank port 226 with the pressure at the tank port 226,balancing forces acting vertically (into and out of the view shown inFIG. 2) on the slider 212. A second opening 234 through the slider 212forms an internal volume that is always in communication with the secondload port 230.

A web 236 between the second opening 234 and the first opening 232permits or prevents flow between the second load port 230 and the tankport 226 depending upon the position of the slider 212. In theillustrated position, the web 236 prevents flow between the second loadport 230 and the tank port 226. When the web 236 moves to the right (asviewed in FIG. 2), a fluid pathway between the second load port 230 andthe tank port 226 is opened, venting any pressure present at the secondload port 230 to the low pressure reservoir connected to the tank port226.

A third opening 238 through the slider 212 permits the fluid volume inthe trough above the first load port 228 to equalize with the pressureat the first load port 228, which balances forces acting vertically(into and out of the view shown in FIG. 2) on the slider 212. A web 240between the second opening 234 and the third opening 238 prevents flowbetween the supply port 224 and the second load port 230 in allpositions of the slider 212.

A web 242 between the third opening 238 and the counter surface 222permits or prevents flow between the supply port 224 and the first loadport 228, depending upon the position of the slider 212. In theillustrated position, the web 242 prevents flow between the supply port224 and the first load port 228. When the slider 212 moves to the left(as viewed in FIG. 2), a fluid pathway opens between the supply port 224and the first load port 228, supplying pressurized fluid to the loadconnected to the first load port 228.

The slider 212 cooperates with the walls of the cavity 214 to define thepiloted chamber 220 between the piloted surface 222 and the opposingwall of the cavity 214. A counter chamber 244 is defined between thecounter surface 222 and the opposing wall of the cavity 214. The counterchamber 244 is in fluid communication with the first load port 228 atall times. Additionally, two volumes 246 and 248 may be defined betweenrespective pairs of shoulders of the T-shaped plate forming the slider212 and the shoulders of the T-shaped cavity 214. The volumes 246 and248 are in communication with the tank port 226 at all times. In thismanner, a hydraulic lock of the slider 212 is prevented.

The total area of the piloted surface 216 of the slider 212 is largerthan the total area of the counter surface 222 of the slider 212.Therefore, when the pressures in the piloted chamber 220 and the counterchamber 244 are equal, the resultant unbalanced net force acting on theslider 212 will urge the slider 212 to the left (as viewed in FIG. 2).

The exact configuration of the ports and openings shown in theMEMS-based spool valve 200 and the slider 212 is not required. TheMEMS-based spool valve 200 is configured to receive a relatively-smallpilot signal, such as the pilot signal from the MEMS microvalve 100, andoutput a stronger signal (either for control or further piloting) to theload. When referring to fluidic signals, such as the pilot signalreceived by the MEMS-based spool valve 200, the term small may generallyrefer to relatively low flow volumetric flow. Therefore, the MEMS-basedspool valve 200 amplifies the pilot signal and allows the pilot signalto control or pilot devices requiring higher flow or higher pressurethan provided by the pilot signal alone.

Referring now to FIG. 3A, FIG. 3B, and FIG. 3C, and with continuedreference to FIGS. 1-2, there are shown elements of a transmission 300which may incorporate some of the fluid pressure/flow control systemsdescribed herein. FIG. 3A shows a schematic diagram of the transmission300 having at least one dog clutch mechanism 310.

FIG. 3B shows a schematic isometric view of a synchronized dog clutch330 which may be used within the dog clutch mechanism 310 of thetransmission 300 shown in FIG. 3A. The selector for the synchronized dogclutch 330 is a selector fork 332. FIG. 3C shows a schematicpartial-cutaway, exploded, isometric view of a synchronized dog clutch350 which may be used within the dog clutch mechanism 310 of thetransmission 300 shown in FIG. 3A. The selector for the synchronized dogclutch 350 is an axial piston 352.

The dog clutch mechanism 310—and, more specifically, the synchronizeddog clutch 330 and the synchronized dog clutch 350—may be controlled bya pressure/flow control system 312. Options for the pressure/flowcontrol system 312 are shown in FIGS. 4-7. One or more additionalpressure/flow control systems 312 may be incorporated into thetransmission 300 or the dog clutch mechanism 310.

The transmission 300 transfers torque from an engine (not shown) to thevehicle output (not shown), such as a final drive or a differential. Byselecting a gear ratio or operating mode, the transmission 300 variesthe speed ratio and torque multiplication between a transmission inputmember 314 coupled to the engine and a transmission output member 316coupled to the vehicle output. The transmission 300 may be a dual-clutchtransmission (DCT), a manual transmission, an automatic-manualtransmission, an automatic transmission, or a hybrid transmission.

One or more dog clutch mechanisms 310 are used to select the differentgear ratios of the transmission 300. A controller 318 may controlactuation of the dog clutch mechanisms 310 with the pressure/flowcontrol system 312 to engage the operating mode selection of the speedratio of the transmission 300. The dog clutch mechanism 310 may also beused in transfer cases, four-wheel drive selection, or other situationsrequiring selective coupling of two or more rotating shafts or members.

The controller 318 may include multiple devices and may includedistributed controller architecture, such as the microprocessor-basedelectronic control unit (ECU). The controller 318 may include one ormore components with a storage medium and a suitable amount ofprogrammable memory, which are capable of storing and executing one ormore algorithms or methods to effect control of the transmission 300 orcomponents thereof. Furthermore, the controller 318 may be configured toprovide the electric current which selectively and variably actuates theMEMS microvalve 100 shown in FIG. 1.

The transmission 300 may include a lube regulating valve (not shown)configured to control the flow of hydraulic fluid for lubrication of thetransmission 300. The lube regulating valve may also control the flow ofhydraulic fluid for cooling of the transmission 300. The transmission300 may also include a line pressure control valve (not shown)configured to control the base pressure of hydraulic fluid in thetransmission 300. The line pressure control valve providesconsistently-pressurized fluid from the pump to many components of thetransmission 300.

As shown in FIGS. 3B and 3C, the dog clutch mechanism 310 may includedifferent types of torque transmitting mechanisms, such as thesynchronized dog clutch 330 shown in FIG. 3B and the synchronized dogclutch 350 shown in FIG. 3C. Generally, dog clutches provide non-slipcoupling of, and torque transfer between, two rotating members. Unlikefriction plate clutches, for example, dog clutches may not be intendedfor slipping engagement.

Depending upon the type of transmission 300 and the rotating memberswith which it is interacting, the dog clutch mechanism 310 shown in FIG.3A may be the synchronized dog clutch 330, the synchronized dog clutch350, or another type of dog clutch mechanism. In each of the illustratedconfigurations, the dog clutch mechanism 310 may be controlled by thepressure/flow control system 312 and any of the options thepressure/flow control system 312 described herein with respect to FIGS.4-7.

Referring now to FIG. 3B, the synchronized dog clutch 330 uses theselector fork 332 to selectively mechanically couple a dog input 334 toa dog output 336. The dog input 334 and the dog output 336 rotate abouta common axis in the configuration shown in FIG. 3B. Engagement of thesynchronized dog clutch 330 occurs through intermeshing sets of teeth(dog teeth) which are rotating in common with the dog input 334 and withthe dog output 336.

Generally, before engagement of the synchronized dog clutch 330, the dogclutch mechanism 310 will be unloaded, such that it is not carryingsubstantial amounts of torque across the synchronized dog clutch 330.However, to facilitate engagement, the dog input 334 and the dog output336 may need to be rotating at substantially the same speed. Asynchronizer 338 (also referred to as a synchromesh) is attached to theselector fork 332 and brings the dog input 334 and the dog output 336 tosubstantially similar rotating speeds before final engagement.

The synchronizer 338 allows limited slipping engagement while the doginput 334 and the dog output 336 are being synchronized or aligned. Thismay occur through gradual frictional engagement of cones within thesynchronizer 338. As the cones of the synchronizer 338 come intocontact, friction brings the rotation of the dog input 334 and the dogoutput 336 to substantially the same speed, such that the dog input 334and the dog output 336 are synchronized.

The selector fork 332 is actuated along the common axis of the dog input334 and the dog output 336 by a fork piston 340. The fork piston 340 isin fluid communication with the pressure/flow control system 312.Depending upon the configuration of the fork piston 340 and the selectorfork 332, either engagement or disengagement of the synchronized dogclutch 330 may occur in response to increased pressure within the forkpiston 340. The synchronized dog clutch 330 may include a return spring(not shown) to oppose the movement created by increased pressure withinthe fork piston 340. Alternatively, the fork piston 340 may beconfigured to provide both engagement and disengagement by selectivelypressurizing opposing chambers within the fork piston 340 to selectivelymove the selector fork 332 in opposing directions. Furthermore, insteadof simply engaging or disengaging the dog output 336 to the dog input334, the synchronized dog clutch 330 may be used to selectively couplethe dog input 334 to one of two or more different dog outputs.

Because the synchronized dog clutch 330 is not generally used forprolonged slipping engagement, control of the fork piston 340 may bethrough an on/off signal, as opposed to a regulated signal. To providethe on/off signal, the fork piston 340 may be coupled to an on/off valve(not shown), or the pressure/flow control system 312 may be configuredto directly provide the on/off signal.

Referring now to FIG. 3C, the synchronized dog clutch 350 uses the axialpiston 352 to selectively mechanically couple a dog input 354 to a dogoutput 356. The dog input 354 and the dog output 356 rotate about acommon axis in the configuration shown in FIG. 3C. Engagement of thesynchronized dog clutch 350 occurs through intermeshing sets of teeth(dog teeth) which are rotating in common with the dog input 354 and withthe dog output 356.

Generally, before engagement of the synchronized dog clutch 350, the dogclutch mechanism 310 will be unloaded, such that it is not carryingsubstantial amounts of torque across the synchronized dog clutch 350.However, to facilitate engagement, the dog input 354 and the dog output356 may need to be rotating at substantially the same speed. Asynchronizer 358 (or synchromesh) is disposed between the dog input 354and the dog output 356 and may include multiple components. As the axialpiston 352 is actuated, the synchronizer 358 brings the dog input 354and the dog output 356 to substantially similar rotating speeds beforefinal engagement.

The synchronizer 358 may allow some slipping engagement while the doginput 354 and the dog output 356 are being synchronized or aligned. Thismay occur through gradual frictional engagement of cones within thesynchronizer 358. As the cones of the synchronizer 358 come intocontact, friction brings the rotation of the dog input 354 and the dogoutput 356 to substantially the same speed, such that the dog input 354and the dog output 356 are synchronized.

The axial piston 352 is actuated along the common axis of the dog input354 and the dog output 356 by fluid pressure acting on the axial piston352. Depending upon the configuration of the axial piston 352, eitherengagement or disengagement of the synchronized dog clutch 350 may occurin response to increased pressure transferred to the axial piston 352from an adjacent chamber (not shown). The synchronized dog clutch 350may include a return spring (not shown) to oppose the movement createdby increased pressure on the axial piston 352.

Because the synchronized dog clutch 350 is not generally used forprolonged slipping engagement, control of the axial piston 352 may bethrough an on/off signal, as opposed to a regulated signal. To providethe on/off signal, the axial piston 352 may be coupled to the on/offvalve (not shown), or the pressure/flow control system 312 may beconfigured to directly provide the on/off signal.

Referring now to FIGS. 4-7, and with continued reference to FIGS. 1-3C,there are shown schematic box diagrams of options for pressure/flowcontrol systems for dog clutches, such as the dog clutch mechanism 310shown in FIG. 3A, the synchronized dog clutch 330 shown in FIG. 3B, andthe synchronized dog clutch 350 shown in FIG. 3C. Each of the pluralityof options for pressure/flow control systems shown and described may beused for operation and control of the dog clutch mechanism 310. Each ofthe options may be substituted into the pressure/flow control systems312 diagrammatically shown in FIG. 3A to control the dog clutchmechanism 310 and, more specifically, the synchronized dog clutch 330and the synchronized dog clutch 350.

FIG. 4 shows a first option 400 for a pressure/flow control system for ahydraulically-actuated component 410 within the transmission 300. Thefirst option 400 includes a pilot valve 412 controlling a regulatingvalve 414. The regulating valve 414 is in fluid communication with thepilot valve 412. The pilot valve 412 includes a first valve 416producing a pilot signal. The regulating valve 414 is configured toreceive the pilot signal and the regulating valve 414 is configured tooutput a control signal which controls the hydraulically-actuatedcomponent 410.

The hydraulically-controlled component 410 may be either of thesynchronized dog clutch 330 and the synchronized dog clutch 350 shown inFIGS. 3B and 3C, respectively. For example, and without limitation, thecontrol signal from the regulating valve 414 may be sent directly to thefork piston 340 or the axial piston 352. Alternatively, the controlsignal from the regulating valve 414 may be sent to the on/off valve,where the control signal is converted to the on/off signal before beingsent to the fork piston 340 or the axial piston 352. In either of theillustrated configurations, engagement and disengagement are controlledbased upon the control signal from the regulating valve 414, which isproduced in response to the pilot signal from the pilot valve 412.

In the first option 400 shown in FIG. 4, the first valve 416 may includethe MEMS microvalve 100 shown in FIG. 1, and the regulating valve 414may include the MEMS-based spool valve 200. Therefore, as describedherein, the MEMS microvalve 100 produces the pilot signal andcommunicates through the pilot port 120 to the piloted chamber 220 ofthe MEMS-based spool valve 200.

As shown in FIGS. 1 and 2, when the MEMS microvalve 100 is combined withthe MEMS-based spool valve 200, either by attaching the two directlytogether or by fluidly connecting the pilot port 120 and the pilotedchamber 220, the MEMS microvalve 100 acts on the MEMS-based spool valve200 to alter the fluid flow and pressure to the first load port 228 andthe second load port 230.

The inlet port 116 in the MEMS microvalve 100 is relatively small incomparison to the supply port 224 and the first load port 228 of theMEMS-based spool valve 200. In combined operation, the beam 112 of theMEMS microvalve 100 uncovers the inlet port 116, and fluid flows throughthe inlet port 116, the first chamber 122, and the outlet orifice 124 tothe outlet port 118. The inlet port 116 may act as an additional orificein this flow path.

Due to possible pressure drop through the inlet port 116, it may not bepossible to get the pressure in the piloted chamber 220 of theMEMS-based spool valve 200 up to the pressure provided by thehigh-pressure fluid source. The pressure in the counter chamber 244 mayachieve a higher pressure (at or near pump outlet pressure) than may beachieved in the piloted chamber 220, owing to the larger openings of thesupply port 224 and the first load port 228 of the MEMS-based spoolvalve 200, and resultant low pressure drop when fluid flows throughthese ports. However, because the surface area of the piloted surface216 is greater than the surface area of the counter surface 222, theslider 212 can still be moved leftward (as viewed in FIG. 2) even if thepressure in the piloted chamber 220 acting on the piloted surface 216 isless than the pressure in the counter chamber 244.

The MEMS-based spool valve 200 has three principal zones or positions ofoperation: a pressure increase position, a pressure hold position, and apressure decrease position. The MEMS-based spool valve 200 is shown inFIG. 2 in the pressure hold position, such that the MEMS-based spoolvalve 200 is holding pressurized fluid on the hydraulically-actuatedcomponent 410 (the load).

If the slider 212 is moved rightward (as viewed in FIG. 2), theMEMS-based spool valve 200 is in the pressure decrease position. This isaccomplished when the controller 318 commands the MEMS microvalve 100 toclose, by increasing electric current supplied to the actuator 114. Thefirst and second ribs 132 and 134 of the actuator 114 expand, causingthe beam 112 to pivot counter-clockwise (bending the flexure pivot 126)and cover more of the inlet port 116. Flow decreases through the firstchamber 122 from the inlet port 116 to the outlet port 118. The pressuredrop across the outlet orifice 124 decreases.

The MEMS microvalve 100 shown defaults to the open position, which maybe referred to as a “normally high” or “normally on” valve.Alternatively, the MEMS microvalve 100 may be configured close bydecreasing the electric current supplied to the actuator 114, such thatthe MEMS microvalve 100 would default to the closed position, which maybe referred to as a “normally low” or “normally off” valve.

Pressure in the first chamber 122 and the pilot port 120 also decreases.Because the pilot port 120 is in direct fluid communication with thepiloted chamber 220, this results in an imbalance of the forces actingon the slider 212. The decreased force acting on the piloted surface 216(due to the lowered pressure in the piloted chamber 220) is now lessthan the unchanged force acting on the counter surface 222 due to thepressure in the counter chamber 244 (connected to the load).

The force imbalance urges the slider 212 of the MEMS-based spool valve200 to the right (as viewed in FIG. 2). The web 236 is thus movedrightward, permitting flow of pressurized fluid from thehydraulically-controlled component 410, through the second load port 230and through the second opening 234 in the slider 212. From there, someof the flow passes directly out of the tank port 226, while some flowmay pass up into the trough above the tank port 226, over the top of theweb 236, down through the first opening 232 and out the tank port 226.In this manner, pressure is released from the hydraulically-controlledcomponent 410 and vented to the low pressure reservoir connected to thetank port 226.

The slider 212 of the MEMS-based spool valve 200 will move back to thepressure hold position when the pressure in the counter chamber 244(acting through the first load port 228) is decreased such that forcesacting on the slider 212 urge the slider 212 leftward (as viewed in FIG.2). With forces equalized, the slider 212 of the MEMS-based spool valve200 will stop in the pressure hold position. Thus, the pressure at theload (as sensed through the first load port 228 and the second load port230) will be proportionate to the electrical signal (current) suppliedto the actuator 114.

To move the MEMS-based spool valve 200 into the pressure increaseposition, the controller 318 decreases current flow through the ribs ofthe actuator 114 and the beam 112 of the MEMS microvalve 100 pivotsclockwise to uncover more of the inlet port 116. This results in apressure increase in the piloted chamber 220, while the pressure in thecounter chamber 244 remains constant. The slider 212 is moved leftward(as viewed in FIG. 2) due to the resultant imbalance of forces acting onthe slider 212. If the MEMS-based spool valve 200 was in the pressuredecrease position, the leftward movement moves the slider valve back tothe pressure hold position shown in FIG. 2.

If the controller 318 further decreases current flow and causes the MEMSmicrovalve 100 to open further, the pressure in the piloted chamber 220further increases, urging the slider 212 of the MEMS-based spool valve200 further leftward (as viewed in FIG. 2) into the pressure increaseposition. The web 242 is moved leftward, permitting flow of pressurizedfluid from the supply port 224 through the third opening 238 in theslider 212. From the third opening 238, some of the flow passes directlyout of the first load port 228, while some flow may pass up into thetrough over the top of the web 242, through the second counter chamber244 and out of the first load port 228. In this manner, pressure isdirected from the source of high-pressure fluid connected to the supplyport 224 and applied to the load connected to the first load port 228(e.g., the hydraulically-operated component 410).

The control signal produced by the MEMS-base spool valve 200 may havesufficient pressure and flow characteristics to control thehydraulically-controlled component 410 with a relatively-short responsetime. Alternatively, the pilot signal produced by the MEMS microvalve100 may be able to directly control the hydraulically-controlledcomponent 410 without amplification. However, the response times fromdirectly controlling the hydraulically-controlled component 410 with theMEMS microvalve 100 may be relatively slower than when combined with theMEMS-based spool valve 200 or another amplifying valve (throughincreases in flow).

As also shown in FIG. 4, the first option 400 further includes a MEMSpressure transducer 420. The MEMS pressure transducer 420 is optional.However, when used, the MEMS pressure transducer 420 is configured tosense the pressure profile of the control signal from the regulatingvalve 414. The controller 318, or other control device, may beconfigured to receive input from the MEMS pressure transducer 420 and toprovide output to the MEMS microvalve 100 in the pilot valve 412 toregulate the system pressure in response to input from the MEMS pressuretransducer 420. Therefore, with the MEMS pressure transducer 420 and thecontroller 318, the first option 400 may be configured for closed-loopfeedback and adjustment of the control signal sent to thehydraulically-controlled component 410. Alternatively, since the dogclutch mechanism 310 may use on-off actuation, the MEMS Pressuretransducer 420 may be used to determine if the on pressure has reachedthe desired level to move and hold the selector fork 332 or the axialpiston 352.

FIG. 5 shows a second option 500 for a pressure/flow control system fora hydraulically-actuated component 510 within the transmission 300. Thesecond option 500 includes a pilot valve 512 controlling a regulatingvalve 514. The regulating valve 514 is in fluid communication with thepilot valve 512.

The pilot valve 512 includes a first valve 516 producing a pilot signal.However, unlike the first option 400 shown in FIG. 4, in the secondoption 500 the pilot valve 512 also includes a second valve 518, whichsteps up or amplifies the pilot signal to an amplified pilot signal. Theregulating valve 514 is configured to receive the amplified pilot signaland the regulating valve 514 is configured to output a control signal,which controls the hydraulically-actuated component 510.

In the second option 500 shown in FIG. 5, the first valve 516 mayinclude the MEMS microvalve 100 shown in FIG. 1 and the second valve 518may include the MEMS-based spool valve 200. Therefore, as alreadydescribed herein, the MEMS microvalve 100 selectively produces the pilotsignal and communicates through the pilot port 120 to the pilotedchamber 220 of the MEMS-based spool valve 200. However, with the secondoption 500, the output of the MEMS-based spool valve 200 is theamplified pilot signal, which is then used by the regulating valve 514.

In the second option 500 shown in FIG. 5, the regulating valve 514 is aconventional mechanical regulating valve. Generally, the conventionalmechanical regulating valve is a regulating valve produced by mechanicalmachining processes, as opposed to the micromachining processes used toproduce MEMS-based devices. Based upon the amplified pilot signalprovided by the pilot valve 512, the conventional mechanical regulatingvalve provides the control signal for the hydraulically-actuatedcomponent 510.

The amplified pilot signal produced by the pilot valve 512 (includingboth the first valve 516 and the second valve 518) may have sufficientpressure and flow characteristics to control the conventional mechanicalregulating valve, which may then control the hydraulically-controlledcomponent 510. However, the pilot signal produced by the first valve 516(the MEMS microvalve 100) of the pilot valve 512 would may not be ableto directly pilot the conventional mechanical regulating valve withoutdelaying the response time. While the MEMS microvalve 100 may be able todirectly control the hydraulically-controlled component 510, theresponse time may be limited due to the limited flow passing through theMEMS microvalve 100. The conventional mechanical regulating valvefurther increases the pressure and flow characteristics used to controlthe hydraulically-controlled component 510, as compared to the firstoption 400 shown in FIG. 4.

Similar to the first option shown in FIG. 4, the second option 500 mayfurther include one or more optional MEMS pressure transducers 520.However, when used, the MEMS pressure transducers 520 are configured tosense the pressure profile of the amplified pilot signal from the pilotvalve 512 or of the control signal from the regulating valve 514. Inmost configurations, only one of the MEMS pressure transducers 520 willbe used. If used to sense the pressure profile of the pilot signal, theMEMS pressure transducer 520 may be packaged into a single package alongwith the MEMS microvalve 100 and the MEMS-based spool valve 200 for thepilot valve 512.

The controller 318, or other control device, is configured to receiveinput from one or more of the MEMS pressure transducers 520 and toprovide output to the MEMS microvalve 100 in the pilot valve 512 toregulate the system pressure in response to input from one of the MEMSpressure transducers 520. Therefore, the MEMS pressure transducers 520provide closed-loop feedback and adjustment of the control signal sentto the hydraulically-controlled component 510.

The hydraulically-controlled component 510 may be either of thesynchronized dog clutch 330 and the synchronized dog clutch 350 shown inFIGS. 3B and 3C, respectively. For example, and without limitation, thecontrol signal from the regulating valve 514 may be sent directly to thefork piston 340 or the axial piston 352. Alternatively, the controlsignal from the regulating valve 514 may be sent to the on/off valve,where the control signal is converted to the on/off signal before beingsent to the fork piston 340 or the axial piston 352. In either of theillustrated configurations, engagement and disengagement are controlledbased upon the control signal from the regulating valve 514, which isproduced in response to the amplified pilot signal from the pilot valve512.

FIG. 6 shows a third option 600 for a pressure/flow control system for ahydraulically-actuated component 610 within the transmission 300. Thethird option 600 includes a pilot valve 612 controlling a regulatingvalve 614. The regulating valve 614 is in fluid communication with thepilot valve 612.

The pilot valve 612 includes a first valve 616 producing a pilot signal.The regulating valve 614 is configured to receive the pilot signal andthe regulating valve 614 is configured to output a control signal, whichcontrols the hydraulically-actuated component 610.

In the third option 600 shown in FIG. 6, the first valve 516 may includethe MEMS microvalve 100 shown in FIG. 1, but there is no additionalvalve forming the pilot valve 512. Therefore, unlike the first option400 shown in FIG. 4 and in the second option 500 shown in FIG. 5, theMEMS microvalve 100 communicates the pilot signal directly to theregulating valve 616, which is a small mechanical spool valve.

Generally, the small mechanical spool valve is a regulating valveproduced by mechanical machining processes, but on a smaller scale thanthe conventional mechanical regulating valve. Based upon the(un-amplified) pilot signal provided by the pilot valve 612, the smallmechanical spool valve provides the control signal for thehydraulically-actuated component 610. Compared to the conventionalmechanical regulating valve used in the second option 500 shown in FIG.5, the small mechanical spool valve is, for example, on the order halfof the size of the conventional mechanical regulating valve.

The pilot signal produced by the pilot valve 612 (including only theMEMS microvalve 100) may have sufficient pressure and flowcharacteristics to control the small mechanical spool valve used for theregulating valve 616 with relatively quick response times. While theMEMS microvalve 100 alone may be capable of directly controlling theconventional mechanical regulating valve used in the second option 500,the response times for actuation may be delayed. The small mechanicalspool valve used for the regulating valve 616 in the third option 600may be used to amplify the signal from the MEMS microvalve 100, suchthat the small mechanical spool valve may control thehydraulically-controlled component 610.

The third option 600 may further include one or more optional MEMSpressure transducers 620. However, when used, the MEMS pressuretransducers 620 are configured to sense the pressure profile of thepilot signal from the pilot valve 612 or of the control signal from theregulating valve 614. In most configurations, only one of the MEMSpressure transducers 620 will be used. If used to sense the pressureprofile of the pilot signal, the MEMS pressure transducer 620 may bepackaged into a single package along with the MEMS microvalve 100 forthe pilot valve 612.

The controller 318, or another controller, is configured to receiveinput from one or more of the MEMS pressure transducers 620 and toprovide output to the MEMS microvalve 100 in the pilot valve 612 toregulate the system pressure in response to input from one of the MEMSpressure transducers 620. Therefore, the MEMS pressure transducers 620provide closed-loop feedback and adjustment of the control signal sentto the hydraulically-controlled component 610.

The hydraulically-controlled component 610 may be either of thesynchronized dog clutch 330 and the synchronized dog clutch 350 shown inFIGS. 3B and 3C, respectively. For example, and without limitation, thecontrol signal from the regulating valve 614 may be sent directly to thefork piston 340 or the axial piston 352. Alternatively, the controlsignal from the regulating valve 614 may be sent to the on/off valve,where the control signal is converted to the on/off signal before beingsent to the fork piston 340 or the axial piston 352. In either of theillustrated configurations, engagement and disengagement are controlledbased upon the control signal from the regulating valve 614, which isproduced in response to the pilot signal from the pilot valve 612.

FIG. 7 shows a fourth option 700 for a pressure/flow control system fora hydraulically-actuated component 710 within the transmission 300. Thefourth option 700 includes a pilot valve 712 controlling a regulatingvalve 714. The regulating valve 714 is in fluid communication with thepilot valve 712.

The pilot valve 712 includes a first valve 716 producing a pilot signal.Similar to the second option 500 shown in FIG. 5, the pilot valve 712also includes a second valve 718, which steps up, or amplifies, thepilot signal to an amplified pilot signal. The regulating valve 714 isagain configured to receive the amplified pilot signal and theregulating valve 714 is configured to output a control signal, whichcontrols the hydraulically-actuated component 710.

In the fourth option 700 shown in FIG. 7, the first valve 716 mayinclude the MEMS microvalve 100 shown in FIG. 1. However, the secondvalve 718 is a small mechanical spool valve. The regulating valve 714 isagain a conventional mechanical regulating valve. Based upon theamplified pilot signal provided by the pilot valve 712, the conventionalmechanical regulating valve provides the control signal for thehydraulically-actuated component 710.

Therefore, as already described herein, the MEMS microvalve 100selectively produces the pilot signal and communicates through the pilotport 120 to the small mechanical spool valve. However, with the fourthoption 700, the output of the small mechanical spool valve is theamplified pilot signal, which is then used by the regulating valve 714.In the fourth option 700, the small mechanical spool valve used as thesecond valve 718 functions similarly to the MEMS-based spool valve 200used as the second valve 518 in the second option 500 shown in FIG. 5.However, the small mechanical spool valve used as the second valve 718for the fourth option 700 may be at least one-hundred times larger thanthe MEMS-based spool valve 200 used for the second valve 518 in thesecond option 500.

The amplified pilot signal produced by the pilot valve 712 (includingboth the first valve 716 and the second valve 718) has sufficientpressure and flow characteristics to control the conventional mechanicalregulating valve, which may then control the hydraulically-controlledcomponent 710. The pilot signal produced by the first valve 716 alone(the MEMS microvalve 100) may not be able to directly pilot theconventional mechanical regulating valve or may not be able to directlycontrol the hydraulically-controlled component 710 without causing adelayed response due to the low-volume flow from the MEMS microvalve100. The conventional mechanical regulating valve further increases thepressure and flow characteristics used to control thehydraulically-controlled component 710.

The fourth option 700 may further include one or more MEMS pressuretransducers 720. The MEMS pressure transducers 720 are again optional.However, when used, the MEMS pressure transducers 720 are configured tosense the pressure profile of the amplified pilot signal from the pilotvalve 712 or of the control signal from the regulating valve 714. Inmost configurations, only one of the MEMS pressure transducers 720 willbe used.

The controller 318, or other controller, is configured to receive inputfrom one or more of the MEMS pressure transducers 720 and to provideoutput to the MEMS microvalve 100 in the pilot valve 712 to regulate thesystem pressure in response to input from one of the MEMS pressuretransducers 720. Therefore, the MEMS pressure transducers 720 provideclosed-loop feedback and adjustment of the control signal sent to thehydraulically-controlled component 710.

The hydraulically-controlled component 710 may be either of thesynchronized dog clutch 330 and the synchronized dog clutch 350 shown inFIGS. 3B and 3C, respectively. For example, and without limitation, thecontrol signal from the regulating valve 714 may be sent directly to thefork piston 340 or the axial piston 352. Alternatively, the controlsignal from the regulating valve 714 may be sent to the on/off valve,where the control signal is converted to the on/off signal before beingsent to the fork piston 340 or the axial piston 352. In either of theillustrated configurations, engagement and disengagement are controlledbased upon the control signal from the regulating valve 714, which isproduced in response to the pilot signal from the pilot valve 712.

The detailed description and the drawings or figures are supportive anddescriptive of the invention, but the scope of the invention is definedsolely by the claims. While some of the best modes and other embodimentsfor carrying out the claimed invention have been described in detail,various alternative designs and embodiments exist for practicing theinvention defined in the appended claims.

1. A pressure and flow control system for a dog clutch comprising: apilot valve including a first valve, wherein the pilot valve isconfigured to produce a pilot signal and the first valve is a MEMSmicrovalve; a regulating valve in fluid communication with the pilotvalve, wherein the regulating valve is configured to receive the pilotsignal and is configured to output a control signal; and a selectorconfigured to engage and disengage the dog clutch in response to thecontrol signal.
 2. The pressure and flow control system of claim 1,wherein the pilot valve further includes a second valve and theregulating valve is a conventional mechanical regulating valve.
 3. Thepressure and flow control system of claim 2, wherein the second valve isa MEMS-based spool valve.
 4. The pressure and flow control system ofclaim 2, wherein the second valve is a small mechanical spool valve. 5.The pressure and flow control system of claim 1, wherein the regulatingvalve is a MEMS-based spool valve.
 6. The pressure and flow controlsystem of claim 1, wherein the regulating valve is a small mechanicalspool valve.
 7. The pressure and flow control system of claim 3, furthercomprising a MEMS pressure transducer, wherein the MEMS pressuretransducer is configured to sense the pressure profile of one of thepilot signal and the control signal.
 8. The pressure and flow controlsystem of claim 7, further comprising a controller, wherein thecontroller is configured to receive input from the MEMS pressuretransducer and to provide output to the pilot valve to regulate thesystem pressure in response to input from the MEMS pressure transducer.9. The pressure and flow control system of claim 8, wherein thecontroller is configured to provide an electronic current, and whereinthe pilot valve is configured to produce the pilot signal in response tothe electronic current.
 10. The pressure and flow control system ofclaim 9, wherein the selector is configured to engage and disengage thedog clutch in response to an on/off signal, and wherein the controlsignal from the regulating valve is configured as the on/off signal. 11.The pressure and flow control system of claim 9, further comprising anon/off valve disposed between the regulating valve and the selector,wherein the selector is configured to engage and disengage the dogclutch in response to an on/off signal, and wherein the on/off valve isconfigured to convert the control signal to the on/off signal.
 12. Thepressure and flow control system of claim 6, further comprising a MEMSpressure transducer, wherein the MEMS pressure transducer is configuredto sense the pressure profile of one of the pilot signal and the controlsignal.
 13. The pressure and flow control system of claim 12, furthercomprising a controller; wherein the controller is configured to receiveinput from the MEMS pressure transducer and to provide output to thepilot valve to regulate the system pressure in response to input fromthe MEMS pressure transducer.
 14. The pressure and flow control systemof claim 13, wherein the controller is configured to provide anelectronic current, and wherein the pilot valve is configured to producethe pilot signal in response to the electronic current.
 15. The pressureand flow control system of claim 14, wherein the selector is configuredto engage and disengage the dog clutch in response to an on/off signal,and wherein the control signal from the regulating valve is configuredas the on/off signal.
 16. The pressure and flow control system of claim14, further comprising an on/off valve disposed between the regulatingvalve and the selector, wherein the selector is configured to engage anddisengage the dog clutch in response to an on/off signal, and whereinthe on/off valve is configured to convert the control signal to theon/off signal.
 17. A pressure and flow control system for a dog clutchcomprising: a pilot valve including a MEMS microvalve and a MEMS-basedspool valve, wherein the pilot valve is configured to produce aamplified pilot signal; a conventional mechanical regulating valve influid communication with the pilot valve, wherein the regulating valveis configured to receive the amplified pilot signal and is configured tooutput a control signal; a selector configured to engage and disengagethe dog clutch in response to the control signal; and a controllerconfigured to provide an electronic current, wherein the pilot valve isconfigured to produce the amplified pilot signal in response to theelectronic current.
 18. The pressure and flow control system of claim17, further comprising a MEMS pressure transducer, wherein the MEMSpressure transducer is configured to sense the pressure profile of oneof the amplified pilot signal and the control signal.